Emsi’s ZIP code names are provided by the U.S. Post Office and are included in Analyst as an aid to understanding (generally) where a ZIP code is located. However, the city name associated with a ZIP code should not be taken to mean that the ZIP code is part of the city named. At most, it indicates that the ZIP code is near the city named.
If your analysis requires identifying ZIP codes that match municipal boundaries, it is best to use another source to establish the correct list of ZIPs, then approach Emsi’s tools with that list. If you’re analyzing a functional economy or a functional labor shed, the Radius From Address and Drive Time region selection options in Analyst and Developer are easy ways to create useful regions that can also be edited visually.